Following the dosage instructions of your doctor is the best way to use any medication.
However normally one dose of the drug is to be taken a day. In some case 2 doses can also be taken if directed by your doctor.

Drug Class and Mechanism

Imitrex is classified as an antimigraine medicine. Migraine headaches are caused due to the dilation of blood vessels. It works by constricting the blood vessels in the head. It does not cure migraine and only helps to reduce headache.

Missed Dose

Since this medicine is taken only when needed, missing a dose is not a problem.

Storage

Store Imitrex at room temperature (read medicine label if unsure). Always keep it in a cool dark place that is not directly exposed to sources of heat or moisture and sunlight. Protect it from kids and pets.

Warning/Precautions

Doctors advise against using Imitrex if you are allergic to any ingredient in it or if you have conditions like allergy to Imitrex, Raynaud syndrome, strokes in the past, certain types of heart disease, transient ischemic attacks, uncontrolled blood pressure, peripheral vascular disease.

Discuss your past/current medical history in detail with your doctor before beginning treatment with any new medication. If you have high cholesterole or high blood pressure, diabetes or you smoke heavily then mention it to your doctor before using this medicine.